netdev - Re: NETIF_F_GSO_SOFTWARE vs NETIF_F

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Message-ID: <1446738967.4184.35.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 05 Nov 2015 07:56:07 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Jason A. Donenfeld" <Jason@...c4.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: NETIF_F_GSO_SOFTWARE vs NETIF_F_GSO

On Thu, 2015-11-05 at 16:00 +0100, Jason A. Donenfeld wrote:

> Right -- I saw the expansion in the header file -- it gets the various
> TSOs plus UFO. So what this means is that the packet hasn't yet been
> split up? So were I to add this option, then my driver would have to
> be responsible for splitting up the super-packets manually? In which
> case, there would be no performance benefit in using it, since GSO
> already does this just prior to ndo_start_xmit? Or would there be a
> performance benefit in receiving the super-packets and splitting them
> myself?

It is a performance benefit only if you use the helpers from
net/core/tso.c as some drivers already do.

Otherwise, calling the skb_gso_segment() from your driver has no gain
compared to the one done from core networking stack.


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